1. Field of the Invention
This invention relates to a process for making high moisture content soap bars.
2. Description of the Related Art
Soap in bar form has long been in use for cleansing purposes. Those skilled in the art use the term soap to designate the reaction product of a carboxylic acid with a base, typically a metal hydroxide or carbonate. The resulting salt has both a polar hydrophilic end and a non-polar lipophilic end which facilitates the removal of oils and other non-polar materials from the skin or other surface in the presence of water.
Bar soaps are customarily prepared either by framing/casting or by refining/plodding. Framed or cast soaps are prepared by reacting an appropriate fat, oil or carboxylic acid with a base in the presence of water to form soap, pouring the molten soap containing about 30% water into a frame or a mold, allowing the soap to cool and harden, and removing the soap having about 20% to 25% water by weight in a bar form. Those skilled in the soap-making art are aware that the carboxylic acid hereafter referred to as a fatty acid is readily available as an article of commerce. The fatty acid also can be obtained from a fat, such as tallow or lard, from an oil, such as coconut oil, palm oil, palm kernel oil, or olive oil, or from combinations of fats and oils. Fats and oils are comprised in substantial part of glycerides of varying chain lengths, which are esters of glycerol (glycerine) and fatty acids. Under alkaline conditions, and in the presence of heat, the glycerides constituting the fats and oils break down to form fatty acid salts, also known as soaps, and glycerine.
Refined/plodded soap bars are produced by subjecting the neutralized soap to various finishing steps which alter the crystalline matrix of the soap from the omega phase, as formed in framed/cast soap bars, to the beta phase. A more detailed discussion may be found in Bailey's Industrial Oil And Fat Products, 4th ed., Vol. 1, p. 558 et seq. (1979). Prior to conversion the soap is first dried from a moisture level of approximately 30% to a level in the range of about 10% to about 14%. Next, the dried soap is generally sent to a simple paddle-type mixer where a variety of additives can be introduced. From this mixer the soap is then sent either directly to a refiner or optionally to a three-roll mill and then to the refiner. Both the refiner and the mill subject the soap to compression and an intense shearing action which tend to orient the soap crystals and convert the soap largely to the beta-phase. After refining, the soap is compressed into a dense, coherent form in a plodding operation which forms solid portions which are suitable for stamping into bars.
The drying step is necessary to remove the "gummy" texture and excessive pliability of the soap mass which exist typically at higher moisture levels. In the production of plodded bars, drying to from about 10% to about 14% moisture is necessary to permit the soap mass to be processed through the finishing equipment. Drying on a commercial basis is achieved by several different methods. One procedure employs a water-chilled roll in combination with a second feed roll to spread molten, neutralized soap into a thin, uniform layer. The cooled soap is then scraped from the roll to form chips and dried to a specific moisture level in a tunnel dryer. Soap chips already having a low moisture level (about 10% to 11%) are further dried by repeatedly conducting the chips through close-set water cooled steel rolls (i.e., three-roll mill) in the procedure known as milling described above. A relatively modern technique for the drying of soap is known as spray drying. This process directs molten soap to the top of a tower via spray nozzles. The sprayed soap hardens and then dries in the presence of a current of heated air. Vacuum may be applied to facilitate the removal of water. Though typically the moisture level of plodded soap bars is maintained in the range of about 10% to about 14%, a plodded soap bar containing greater than 14% moisture is known in the prior art.
The incorporation of an alkyl polyglycoside permits the moisture level of the soap bars to be maintained at relatively high levels thereby reducing manufacturing costs by reducing the drying times and drying energy requirements. The presence of an alkyl polyglycoside in a soap produces a bar which exhibits increased flash foaming and a richer and creamier lather. Prior to the present invention, direct incorporation of an alkyl polyglycoside into standard soap making operations which employ tallow/coco soaps made further refining difficult if not impossible. On refining, tallow/coco soaps containing alkyl polyglycosides were found to be too sticky and unsuitable for plodding and stamping.